Heretofore, compositions containing sodium azide have been often used as airbag gas generating agents for occupant-protecting devices in automobiles. However, the toxic effects of sodium azide on the human body [LD50 (oral-rat)=27 mg/kg) and hazardous nature thereof at the time of handling have been perceived as problems. As an alternative to such compositions, therefore, gas generating compositions containing various kinds of nitrogen-containing organic compounds have been developed as so-called non-azide gas generating compositions.
U.S. Pat. No. 4,909,549 discloses a composition that includes a hydrogen-containing tetrazole, a triazole compound and an oxygen-containing oxidizing agent. U.S. Pat. No. 4,370,181 discloses a gas generating composition that includes a metal salt of bitetrazole containing no hydrogen and an oxidizing agent containing no oxygen. U.S. Pat. No. 4,369,079 discloses a gas generating composition that includes a metal salt of bitetrazole containing no hydrogen and alkali metal nitrate; alkali metal nitrite; alkaline earth metal nitrate; alkaline earth metal nitrite or a mixture thereof. U.S. Pat. No. 5,542,999 discloses a gas generating agents that includes fuel such as GZT, triaminonitroguanidine (TAGN), nitroguanidine (NG) or NTO; basic copper nitrate; a catalyst for decreasing toxic gas and a coolant. JP-A 10-72273 discloses a gas generating agent that includes a metal salt of bitetrazole; an ammonium salt of bitetrazole; aminotetrazle and ammonium nitrate.
However, although azide-based gas generating agents generate only nitrogen in general after combustion, non-azide-based gas generating compositions have a disadvantage such that small amounts of toxic carbon monoxide and nitrogen oxides are generated because each of the composition contains carbon, nitrogen and oxygen in general. In addition, compared with the azide-based gas generating agents, the non-azide-based gas generating agents have so high combustion temperatures that they may need a large amount of coolant in actual use. For reducing produced amounts of toxic carbon monoxide and nitrogen oxides after combustion, addition of a metal oxide or a DeNOx agent (a nitrogen-oxide reducing agent) to the gas generating agent is known. For example, in the case of the gas generating composition as disclosed in DE Pat No. 4,401,213, a heavy-metal oxide such as V2O5/MoO3 is added as a catalyst for reducing the produced amounts of toxic carbon monoxide and nitrogen oxides. However, the heavy-metal oxide is considered to be toxic, and addition of a metal oxide leads to a decrease of efficiency of gas generation from the gas generating agent.
WO 98/04507 discloses reduction of the produced amount of a nitrogen oxide in combustion gas by using a combination of a DeNOx agent such as ammonium sulfate, ammonium carbonate or urea and a gas generating agent. However, use of ammonium sulfate will generate toxic sulfur oxide and then ammonium carbonate and urea have problems in their thermal stability. Furthermore, if the DeNOx agents are added, the oxidizing agent in the gas generating agent will be consumed and a produced amount of toxic carbon monoxide is increased.